California's worst power failure started in the Arizona deserts

Replacing faulty equipment at an energy substation triggered events that led to power shortage

The most extensive power outage in California history started in the western Arizona desert.

The replacement of faulty equipment at a power substation apparently triggered a series of events that knocked out Southwest Powerlink, one of two major transmission links that connect the San Diego area to the electrical grid for the western United States.

That, in turn, sent a jolt through the local grid that cut off power at San Onofre Nuclear Generating Station and tripped the other transmission link, this one leading from San Diego north to the Southern California Edison service area.

The result: a full system blackout for 5 million people across San Diego County, southern Orange County, western Arizona and northern Baja California.

The outage exposed weakness in the electricity grid that supplies San Diego County with its power.

The grid is part of a web of powerlines stretching from Canada to northern Baja California, connecting electricity plants with their customers. Because of San Diego’s position in a geographical cul de sac, it is connected to the grid only through two major energy lines: a northern line connected to the San Onofre nuclear plants and an eastern line connected to power plants in Imperial County, Arizona, and northern Mexico.

The problem apparently began at an Arizona substation that is a major delivery point of electricity between power plants in Arizona and San Diego.

Just before 3:30 p.m., a worker at the substation replaced monitoring equipment that had been causing trouble earlier in the day. That created a short-term power outage for about 56,000 customers in Yuma and western Arizona, said APS, Arizona’s largest electric utility, which runs the substation.

Ten minutes later, workers at the substation unsuccessfully tried to restore power to the region, shorting the circuits. That led to a disruption in the electricity lines across Imperial County to San Diego — one of the county’s two major sources of electricity.

“Normally, that should not be a problem,” said Michael Shames, head of Utility Consumers Action Network. “When a power line goes down in the east, you just get your power from the north.”

The worst that should have happened would be temporary, localized “rolling” brownouts or blackouts as the county began to draw power from its second major energy source, the northern powerlines connected to the San Onofre nuclear plants.

But there were no rolling blackouts.

Officials at San Diego Gas & Electric described a “cascading effect” as the electric system shut down.

“There are safeguards built into electrical systems across the country,” said Stephanie Donovan, a spokeswoman for SDG&E. “When the power plant shut off at San Onofre, it was a built-in, automatic protective device. ... The reason that the outage tends to cascade is that the system tried to protect itself from voltage fluctuations.”

Amid a heat wave and surging energy demands, SDG&E engineers worked through Thursday night to execute a “black start” from zero power.

“It’s got to be a very methodic and gradual transition to full power,” said Ali Yari, director of electric transmission and distribution engineering for SDG&E.

California’s Independent System Operator, ISO, is responsible for making sure the amount of electricity generated exactly matches the amount used. An imbalance can trigger a series of uncontrolled blackouts.

The ISO also provides early warnings of possible electricity outages, which allow the public to better prepare for service interruptions.

But that this time there was no warning, according to SDG&E President Mike Niggli, who on the company’s Twitter feed said he’d never seen anything like Thursday’s power failure. He’s been with the utility since 1971.

The outage is still dwarfed by the 2003 northeast blackout, where a cascading series of power-line and electricity-plant failures wiped out power for 50 million people from Ohio to Canada and New York City in the biggest blackout in U.S. history.

In 2001, California’s failed experiment with energy deregulation was widely blamed for six days of rolling blackouts that cut power to more than 3 million customers and shut down refrigerators, ATMs and traffic signals.